11,304 research outputs found
Using propensity score methods to assess causal effects of mothers\u27 dieting behavior on daughters\u27 early dieting behavior
Bayesian methods of astronomical source extraction
We present two new source extraction methods, based on Bayesian model
selection and using the Bayesian Information Criterion (BIC). The first is a
source detection filter, able to simultaneously detect point sources and
estimate the image background. The second is an advanced photometry technique,
which measures the flux, position (to sub-pixel accuracy), local background and
point spread function. We apply the source detection filter to simulated
Herschel-SPIRE data and show the filter's ability to both detect point sources
and also simultaneously estimate the image background. We use the photometry
method to analyse a simple simulated image containing a source of unknown flux,
position and point spread function; we not only accurately measure these
parameters, but also determine their uncertainties (using Markov-Chain Monte
Carlo sampling). The method also characterises the nature of the source
(distinguishing between a point source and extended source). We demonstrate the
effect of including additional prior knowledge. Prior knowledge of the point
spread function increase the precision of the flux measurement, while prior
knowledge of the background has onlya small impact. In the presence of higher
noise levels, we show that prior positional knowledge (such as might arise from
a strong detection in another waveband) allows us to accurately measure the
source flux even when the source is too faint to be detected directly. These
methods are incorporated in SUSSEXtractor, the source extraction pipeline for
the forthcoming Akari FIS far-infrared all-sky survey. They are also
implemented in a stand-alone, beta-version public tool that can be obtained at
http://astronomy.sussex.ac.uk/rss23/sourceMiner\_v0.1.2.0.tar.gzComment: Accepted for publication by ApJ (this version compiled used
emulateapj.cls
The Impact of "Deregulation" on Regulator Behavior: An Empirical Analysis of the Telecommunications Act of 1996
This paper examines how regulators set local prices in response to the changes brought on by the Telecommunications Act of 1996 (“Telecom Act”). We are particularly interested in the extent to which state regulators set prices that promoted efficiency or were influenced by private-interest groups who had secured rents under a regime of regulated monopoly. Using regional Bell operating company (RBOC) data, our empirical results indicate that private interests continue to influence the structure of retail and wholesale prices, although their influence appears to be waning. We find that changes to the regulatory structure, as measured by federal approval of RBOC Section 271 applications that open up markets to competition and universal service subsidies, resulted in a re-balancing of retail prices and lower overall price levels.competition, political contributions, private interest, public interest, regulation, telecommunications, universal service
Calibration of the LIGO displacement actuators via laser frequency modulation
We present a frequency modulation technique for calibration of the
displacement actuators of the LIGO 4-km-long interferometric gravitational-wave
detectors. With the interferometer locked in a single-arm configuration, we
modulate the frequency of the laser light, creating an effective length
variation that we calibrate by measuring the amplitude of the frequency
modulation. By simultaneously driving the voice coil actuators that control the
length of the arm cavity, we calibrate the voice coil actuation coefficient
with an estimated 1-sigma uncertainty of less than one percent. This technique
enables a force-free, single-step actuator calibration using a displacement
fiducial that is fundamentally different from those employed in other
calibration methods.Comment: 10 pages, 5 figures, submitted to Classical and Quantum Gravit
Flavor changing interactions mediated by scalars at the weak scale
The quark and lepton mass matrices possess approximate flavor symmetries.
Several results follow if the interactions of new scalars possess these
approximate symmetries. Present experimental bounds allow these exotic scalars
to have a weak scale mass. The Glashow-Weinberg criterion is rendered
unnecessary. Finally, rare leptonic B meson decays provide powerful probes of
these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234
Low-Altitude Reconnection Inflow-Outflow Observations during a 2010 November 3 Solar Eruption
For a solar flare occurring on 2010 November 3, we present observations using
several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope
followed by inflows sweeping into a current sheet region. The inflows are soon
followed by outflows appearing to originate from near the termination point of
the inflowing motion - an observation in line with standard magnetic
reconnection models. We measure average inflow plane-of-sky speeds to range
from ~150-690 km/s with the initial, high-temperature inflows being the
fastest. Using the inflow speeds and a range of Alfven speeds, we estimate the
Alfvenic Mach number which appears to decrease with time. We also provide
inflow and outflow times with respect to RHESSI count rates and find that the
fast, high-temperature inflows occur simultaneously with a peak in the RHESSI
thermal lightcurve. Five candidate inflow-outflow pairs are identified with no
more than a minute delay between detections. The inflow speeds of these pairs
are measured to be 10^2 km/s with outflow speeds ranging from 10^2-10^3 km/s -
indicating acceleration during the reconnection process. The fastest of these
outflows are in the form of apparently traveling density enhancements along the
legs of the loops rather than the loop apexes themselves. These flows could
either be accelerated plasma, shocks, or waves prompted by reconnection. The
measurements presented here show an order of magnitude difference between the
retraction speeds of the loops and the speed of the density enhancements within
the loops - presumably exiting the reconnection site.Comment: 31 pages, 13 figures, 1 table, Accepted to ApJ (expected publication
~July 2012
Spatial and temporal filtering of a 10-W Nd:YAG laser with a Fabry-Perot ring-cavity premode cleaner
We report on the use of a fixed-spacer Fabry–Perot ring cavity to filter spatially and temporally a 10-W laser-diode-pumped Nd:YAG master-oscillator power amplifier. The spatial filtering leads to a 7.6-W TEMinfinity beam with 0.1% higher-order transverse mode content. The temporal filtering reduces the relative power fluctuations at 10 MHz to 2.8 x 10^-/sqrtHz, which is 1 dB above the shot-noise limit for 50 mA of detected photocurrent
Detecting and characterizing lateral phishing at scale
We present the first large-scale characterization of lateral phishing attacks, based on a dataset of 113 million employee-sent emails from 92 enterprise organizations. In a lateral phishing attack, adversaries leverage a compromised enterprise account to send phishing emails to other users, benefit-ting from both the implicit trust and the information in the hijacked user's account. We develop a classifier that finds hundreds of real-world lateral phishing emails, while generating under four false positives per every one-million employee-sent emails. Drawing on the attacks we detect, as well as a corpus of user-reported incidents, we quantify the scale of lateral phishing, identify several thematic content and recipient targeting strategies that attackers follow, illuminate two types of sophisticated behaviors that attackers exhibit, and estimate the success rate of these attacks. Collectively, these results expand our mental models of the 'enterprise attacker' and shed light on the current state of enterprise phishing attacks
Event Stream Processing with Multiple Threads
Current runtime verification tools seldom make use of multi-threading to
speed up the evaluation of a property on a large event trace. In this paper, we
present an extension to the BeepBeep 3 event stream engine that allows the use
of multiple threads during the evaluation of a query. Various parallelization
strategies are presented and described on simple examples. The implementation
of these strategies is then evaluated empirically on a sample of problems.
Compared to the previous, single-threaded version of the BeepBeep engine, the
allocation of just a few threads to specific portions of a query provides
dramatic improvement in terms of running time
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